Allow actually passing dimensions for OpenAI source

-> make sure the settings change is rejected or the settings task fails when the specified model doesn't support
overriding `dimensions` and the passed `dimensions` differs from the model's default dimensions.

meilisearch-types/src/error.rs

@@ -347,6 +347,7 @@ impl ErrorCode for milli::Error {
                     UserError::InvalidFieldForSource { .. }
                     | UserError::MissingFieldForSource { .. }
                     | UserError::InvalidOpenAiModel { .. }
+                    | UserError::InvalidOpenAiModelDimensions { .. }
                     | UserError::InvalidPrompt(_) => Code::InvalidSettingsEmbedders,
                     UserError::TooManyEmbedders(_) => Code::InvalidSettingsEmbedders,
                     UserError::InvalidPromptForEmbeddings(..) => Code::InvalidSettingsEmbedders,

milli/src/error.rs

@@ -227,6 +227,13 @@ only composed of alphanumeric characters (a-z A-Z 0-9), hyphens (-) and undersco
         source_: crate::vector::settings::EmbedderSource,
         embedder_name: String,
     },
+    #[error("`.embedders.{embedder_name}.dimensions`: Model `{model}` does not support overriding its native dimensions of {expected_dimensions}. Found {dimensions}")]
+    InvalidOpenAiModelDimensions {
+        embedder_name: String,
+        model: &'static str,
+        dimensions: usize,
+        expected_dimensions: usize,
+    },
 }
 
 impl From<crate::vector::Error> for Error {

milli/src/update/settings.rs

@@ -974,6 +974,9 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
                             crate::vector::settings::EmbeddingSettings::apply_default_source(
                                 &mut setting,
                             );
+                            crate::vector::settings::EmbeddingSettings::apply_default_openai_model(
+                                &mut setting,
+                            );
                             let setting = validate_embedding_settings(setting, &name)?;
                             changed = true;
                             new_configs.insert(name, setting);
@@ -1132,14 +1135,25 @@ pub fn validate_embedding_settings(
     match inferred_source {
         EmbedderSource::OpenAi => {
             check_unset(&revision, "revision", inferred_source, name)?;
-            check_unset(&dimensions, "dimensions", inferred_source, name)?;
             if let Setting::Set(model) = &model {
-                crate::vector::openai::EmbeddingModel::from_name(model.as_str()).ok_or(
+                let model = crate::vector::openai::EmbeddingModel::from_name(model.as_str())
-                    crate::error::UserError::InvalidOpenAiModel {
+                    .ok_or(crate::error::UserError::InvalidOpenAiModel {
                         embedder_name: name.to_owned(),
                         model: model.clone(),
-                    },
+                    })?;
-                )?;
+                if let Setting::Set(dimensions) = dimensions {
+                    if !model.supports_overriding_dimensions()
+                        && dimensions != model.default_dimensions()
+                    {
+                        return Err(crate::error::UserError::InvalidOpenAiModelDimensions {
+                            embedder_name: name.to_owned(),
+                            model: model.name(),
+                            dimensions,
+                            expected_dimensions: model.default_dimensions(),
+                        }
+                        .into());
+                    }
+                }
             }
         }
         EmbedderSource::HuggingFace => {

milli/src/vector/settings.rs

@@ -1,6 +1,7 @@
 use deserr::Deserr;
 use serde::{Deserialize, Serialize};
 
+use super::openai;
 use crate::prompt::PromptData;
 use crate::update::Setting;
 use crate::vector::EmbeddingConfig;
@@ -82,7 +83,7 @@ impl EmbeddingSettings {
             Self::MODEL => &[EmbedderSource::HuggingFace, EmbedderSource::OpenAi],
             Self::REVISION => &[EmbedderSource::HuggingFace],
             Self::API_KEY => &[EmbedderSource::OpenAi],
-            Self::DIMENSIONS => &[EmbedderSource::UserProvided],
+            Self::DIMENSIONS => &[EmbedderSource::OpenAi, EmbedderSource::UserProvided],
             Self::DOCUMENT_TEMPLATE => &[EmbedderSource::HuggingFace, EmbedderSource::OpenAi],
             _other => unreachable!("unknown field"),
         }
@@ -90,9 +91,13 @@ impl EmbeddingSettings {
 
     pub fn allowed_fields_for_source(source: EmbedderSource) -> &'static [&'static str] {
         match source {
-            EmbedderSource::OpenAi => {
+            EmbedderSource::OpenAi => &[
-                &[Self::SOURCE, Self::MODEL, Self::API_KEY, Self::DOCUMENT_TEMPLATE]
+                Self::SOURCE,
-            }
+                Self::MODEL,
+                Self::API_KEY,
+                Self::DOCUMENT_TEMPLATE,
+                Self::DIMENSIONS,
+            ],
             EmbedderSource::HuggingFace => {
                 &[Self::SOURCE, Self::MODEL, Self::REVISION, Self::DOCUMENT_TEMPLATE]
             }
@@ -109,6 +114,17 @@ impl EmbeddingSettings {
             *source = Setting::Set(EmbedderSource::default())
         }
     }
+
+    pub(crate) fn apply_default_openai_model(setting: &mut Setting<EmbeddingSettings>) {
+        if let Setting::Set(EmbeddingSettings {
+            source: Setting::Set(EmbedderSource::OpenAi),
+            model: model @ (Setting::NotSet | Setting::Reset),
+            ..
+        }) = setting
+        {
+            *model = Setting::Set(openai::EmbeddingModel::default().name().to_owned())
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, Default, Serialize, Deserialize, PartialEq, Eq, Deserr)]